The present invention relates to machines with moving elements, and more particularly to a system and method for determining the position of the moving elements and for using such position data in controlling such elements.
Packaging machines that form a tube from a web of material are known. In these machines, a portion of the tube is filled with a product, such as fluid or other flowable product. Two, spaced portions on the tube are sealed transversely by a pair of sealing jaws in the packaging machine to form a closed package with the product therein. The tube is then severed through the sealed portions to separate the package from adjacent ones formed by the machine. This type of packaging machine is generally referred to as a form, fill and seal (FFS) machine.
Commonly, each of the packages must be filled with a consistent volume of product. This consistency of volume can be provided by making the individual packages of equal volume when sealed. This is accomplished by forming the transverse seals at equally spaced apart locations along the length of the web. In order to so form the seals, movable elements with the sealing jaws thereon must be monitored and controlled accurately to assure the seals are formed at the correct locations. These systems generally use encoders or resolvers to aid in monitoring and controlling the elements.
One drawback to using encoders and resolvers for position feedback is that systems utilizing this type of feedback require homing to a known position before normal operation can begin. Also, with the increased use of software-based motion control systems, commutation alignment must be completed before the homing process, if soft-ware based commutation with algorithmic initialization is employed. Both these processes require movement of the movable elements, which is undesirable in a web-fed FFS machine, as this initialization process generally involves the rejection of packaging material and/or product. This results in increased manufacturing cost and lower yield on the machine. Therefore it is desirable to provide an improved machine that can quickly initialize and home movable elements on a machine at startup or following a fault condition without these drawbacks.
Some position feedback systems determine the position of a movable element by determining the position of a machine component other than the moveable element. For example, machines can determine the position of an electrical motor, belt, or gear, and infer that the movable element so driven has a position consistent therewith. When the monitored component, for example the belt or gear, does not function properly, the position data for the movable element is not accurate.
Other machines that have linear, open paths have started to utilize a single magnetostrictive linear position sensor to determine the position of various components on the path. These sensors have not been applied to closed-loop paths, such as those used in packaging machines. In addition, a single, magnetostrictive sensor has a limited update speed making its use in high-speed applications problematic.
Thus, there remains a need in the art for a system and method for monitoring moving carriages using sensors and features that do not have the drawbacks of the prior art systems and allow highly accurate and fast monitoring and control of moving carriages.
The present invention is directed to an improved machine, such as for the packaging of product(s) in individual packages on a continuous basis. The machine comprises at least one path, at least two magnetostrictive sensors disposed on the path, at least one movable element mounted for movement on the path, and at least one programmable controller. The programmable controller is operatively associated with each sensor and each movable element, and receives at least one signal from one of the sensor(s). This signal is representative of at least one control variable of at least one of the associated movable elements. In this arrangement, the magnetostrictive sensors can be arranged on the path to partially overlap. Furthermore in this arrangement, three or more magnetostrictive sensors can be used or magnetostrictive sensors of the same or different lengths can be used.
In this arrangement, the movable element includes a magnet operatively associated with the magnetostrictive sensors.
In one embodiment, the machine includes a plurality of movable elements mounted on the path that are movable and positionable independently of one another. In yet another embodiment, the machine further includes at least two, closed paths defined by at least two, separate guide members spaced from one another and a plurality of moving elements are mounted for movement along each of the guide members.
Alternatively, a machine of the present invention also includes at least one magnetostrictive sensor and at least one non-absolute sensor disposed on the path. In this arrangement, a plurality of non-absolute sensors can be used and the non-absolute sensor(s) can be a step and direction type of sensor or an incremental type of sensor, which can be at least one Hall Effect sensor. The machine may include movable elements with magnets operatively associated with the magnetostrictive sensor and another actuation device operatively associated with the non-absolute sensor(s).
The present invention is also directed to a method for determining the position of at least one moveable element on a path, comprising the steps of: providing at least one movable element that is movable on the path, each movable element has at least one magnet mounted thereon, providing at least two magnetostrictive sensors on the path for outputting positional information on each movable element the magnetostrictive sensors are operatively associated with at least one magnet, and providing a first programmable controller electrically connected to the sensor(s). The method further includes the step of the first programmable controller linking the magnetostrictive sensors into a single, continuous, virtual sensor on the path. In this method, a second programmable controller can use the virtual sensor to control the movement of the movable elements. Furthermore, the method can include the step of providing first and second programmable controllers, where the first programmable controller is at least one digital signal processor and the second controller is a motion controller.
This method can further include performing commutation alignment on at least one movable element on the path, when the movable element is stationary. The method can also include determining a known position for at least one movable element on the path, when the movable element is stationary or moving.
The present invention is also directed to a method for using positional information for at least one movable element on a path, comprising the steps of: providing at least one movable element that is movable on the path including at least one magnet mounted thereon, providing at least one magnetostrictive sensor on the path for outputting positional information on each movable element, the magnetostrictive sensor is operatively associated with the magnet, and providing at least one programmable controller electrically connected to each sensor. The method further includes using the positional information from each sensor.
In the method, the step of providing at least one movable element can further include providing a servo-motor with each movable element, wherein the step of using the positional information includes performing commutation alignment on each servo-motor using the positional information from each sensor. Alternatively, the step of using the positional information can include determining a known position for the movable element on the path while the element is stationary or moving. In the method, the step of performing commutation alignment can occur when the associated movable element is stationary or moving.
The method may also include providing at least one non-absolute sensor on the path and determining a known position using information from the non-absolute sensor(s).